Autonomous or partially autonomous vehicles relieve drivers of various driving-related tasks. Such vehicles could use gasoline/ethanol fuel blends. An occasional operator or occupant of such a vehicle may not be able to identify degradation of the vehicle's engine performance due to a misrepresented percentage of the ethanol blend of the fuel. A fuel station, for example, may report that the fuel it is supplying is fifteen percent ethanol, but in actuality the fuel may be twenty percent ethanol. This misrepresentation could cause a vehicle's engine computer to operate the engine using an erroneous value for the ethanol percentage, which can degrade performance and/or damage the engine.